Lyman limit

Fig. 4.6. Comparison of D/H measurements at high redshift from Lyman-limit and damped Lyman-a systems. The measurements come from O Meara et al. (2001 3 Lyman-limit systems and one marginal DLA), Crighton et al. (2004 the highest column density Lyman-limit system), Kirkman et al. (2003 another marginal DLA), Pettini Bowen (2001), Levshakov et al. (2002) and O Meara et al. (2006) (three classical DLAs). There is no convincing evidence for systematic trends with either column density or metallicity up to about 1/30 solar.

Blue and UV light from stellar populations is dominated by young, massive stars which also contribute the lion s share of the Z-elements ( metals ). Evolutionary synthesis computations show that, between the Lyman limit (912 A) and 2000 A or so, the spectrum expressed as Lv is more or less flat (Fig. 12.3). This leads to some rather simple considerations because Iv retains its value (and flatness) when the light is redshifted (see Eq. 12.1), because the degradation in energy is simply taken up by the factor dv on integration (Lilly Cowie 1987). 

Fig. 12.15. Growth of metallicity with time in regions of differing overdensity, corresponding approximately to clusters of galaxies (5 = 103 thick curve), DLA and Lyman-limit systems (5 = 102 thinner curve), moderate-column-density Ly-a clouds (5 = 10 dotted curve) and low-column-density Ly-a clouds (8 = 0 dashed curve), The dot-dashed curve shows the global average. After Cen and Ostriker (1999). Courtesy Renyue Cen.

Lyman limit spect The lower limit of wavelengths of spectral lines in the Lyman series (912 angstrom units), or the corresponding upper limit in frequency, energy of quanta, or wave number (equal to the Rydberg constant for hydrogen). iT-mon, lim-3t ... 

Besides contributing to specific bands in the IR, dust grains are also responsible for very broad absorption, culminating in a peak at 217 nm, and continuously rising beyond into the far UV, observed until the Lyman limit at 91.2 nm in the interstellar extinction curve of our Galaxy. Other galaxies have variants of this extinction... 

Although we have not yet described the modem methods of dealing with theoretical chemistry (quantum mechanics), it is possible to describe many of the properties of atoms. For example, the energy necessary to remove an electron from a hydrogen atom (the ionization energy or ionization potential) is the energy that is equivalent to the series limit of the Lyman series. Therefore, atomic spectroscopy is one way to determine ionization potentials for atoms. 

The ionisation energy of the H atom corresponds to removing the electron from the n = 1 energy level. Determine the convergence limit for the H Lyman series and hence estimate the ionisation energy of the H atom in kJ mol-1. 

Extremely stringent lower limits were reported by Rank (29) in 1968. A spectroscopic detection of the Lyman a(2 p - 1 s) emission line of the quarkonium atom (u-quark plus electron) at 2733 A was expected to be able to show less than 3 108 positive quarks, to be compared with 1010 lithium atoms detected by 2 p - 2 s emission at 6708 A. With certain assumptions (the reader is referred to the original article), less than one quark was found per 1018 nucleons in sea water and 1017 nucleons in seaweed, plankton and oysters. Classical oil-drop experiments (with four kinds of oil light mineral, soya-bean, peanut and cod-liver) were interpreted as less than one quark per 1020 nucleons. Whereas a recent value (18) for deep ocean sediments was below 10 21 per nucleon, much more severe limits were reported (30) in 1966 for sea water (quark/nucleon ratio below 3 10-29) and air (below 5 10-27) with certain assumptions about concentration before entrance in the mass spectrometer. At the same time, the ratio was shown to be below 10 17 for a meteorite. Cook etal. (31) attempted to concentrate quarks by ion-exchange columns in aqueous solution, assuming a position of elution between Na+ and Li+. As discussed in the next section, cations with charge + 2/3 may be more similar to Cs+. Anyhow, values below 10 23 for the quark to nucleon ratio were found for several rocks (e.g., volcanic lava) and minerals. It is clear that if such values below a quark per gramme are accurate, we have a very hard time to find the object but it needs a considerably sophisticated technique to be certain that available quarks are not lost before detection. 

Absorption starts at 1108 A. The banded absorption region 850 to 1108 A corresponds to the transition B1 . -X T. (Lyman bands). The dissociation limit at 844.7 A corresponds to... 

The remainder of this chapter will focus on the use, applicability, and limitations of methods used to estimate Koc. Specific examples using recommended methods for Koc will be presented. The reader is encouraged to examine several previous reviews of sorption estimation techniques (Lyman et al., 1982 Gerstl, 1990 Green and Karickhoff, 1990 Sabljic et al., 1995 Baker et al., 1997 Gawlik et al., 1997). 

There is a significant but subdominant mass in dark baryons. Spheroid stars amount to 10% of the baryons or 0.004 in terms of fDisk stars contribute 5% or 0.002 in Intracluster gas amounts to 5% or fib = 0.002. The Lyman alpha forest (at z 0) contains 29 4% of the baryons or = 0.008. This is all we actually observe in any quantifiable amount. In addition, intermediate temperature intergalactic gas, the so-called warm/hot intergalactic medium (WHIM) has been detected, at a temperature of 105 — 106K. It is estimated from simulations (at z 0) to amount to 30% of the local baryons or f = 0.012, with however a large uncertainty. Indeed the WHIM simulations do not resolve the Jeans mass at the resolution limit, and and the existence of WHIM is purely a theoretical inference, at least in so far as its quantitative fraction is concerned. 

The laser beam is introduced parallel to the axis of the trap and retro-rellected by a mirror at the bottom of the trapping cell (Fig. 2.) A mechanical chopper pulses the laser at typically 1 kHz. The 2S atoms are in the same hyperfine state d and therefore remain trapped. After excitation for a brief period, the population of the 2S level is measured by detecting the Lyman-a fluorescence in an applied electric field. A microchannel plate detector is used to permit single photon detection. Due to the small optical collection efficiency for our geometry, the detection efficiency is limited to 10-5. Nevertheless, signal rates as high a few hundred thousand counts per second laser time have been observed. 

Earlier experiments [15,17,23] aiming to observe delayed Lyman-a X-rays following radiative quenching of thermalized p,p(2S) atoms (Eq. 2) had not found any delayed events. Thus, they seemed to give rather low upper limits for the long-lived metastable pp(2S) population under the assumption that the main decay channel of thermalized pp(2S) atoms is radiative quenching. 

The spin-averaged 2p-level broadening T2p in pH was determined indirectly from the intensity balance between the total Balmer series and the Lyman a transition [10,12], a method which is, however, only strictly valid in the limit of equal widths for all 2p hyperfine levels [8,12,14], No hadronic effects were observed in antiprotonic deuterium because of the weakness of the K transitions due to the enhanced absorption from the pD 1 = 1 states. 

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